user7122335 - 7 months ago 46
C Question

# Can't print out sociable numbers properly

I have a code that finds the sum of the divisors of a number, but I can't get it to apply on my increasing n and print all the numbers respectively.

The code is

``````long div(int n) {
long sum = 0;
int square_root = sqrt(n);

for (int i = 1; i <= square_root; i++) {
if (n % i == 0) {
sum += i;
if (i * i != n) {
sum += n / i;
}
}
}

return sum - n;
}
``````

On my main() I need to have a c number that starts from 1 and goes to my MAXCYC which is 28. The n goes from 2 to MAXNUM which is 10000000. The program needs to find all perfect, amicable and sociable numbers and print them with their respective pairs.

Sample output:

Cycle of length 2: 12285 14595 12285

Cycle of length 5: 12496 14288 15472 14536 14264 12496

``````for (int n = 2; n <= MAXNUM; n++) {

long sum = div(n);
long res = div(sum);
if (res <= MAXNUM) { // Checking if the number is just sociable
int c = 0;

while (c <= MAXCYC && n != res) {
res = div(sum);
c++;
}
if (c <= MAXCYC) {
printf("Cycle of length %d: ", c);

printf("%ld ", sum);
do {
printf("%ld ", res);
res = div(res);
}
while (sum < res);

printf("%ld ", sum);
c += c - 2;
printf("\n");
}
}
}
``````

I only get pairs of cycle length of 1, 2 and nothing above that. Also it doesn't even print it correctly since it says Cycle of length 0: in all of the results without increasing. I think the problem is in the f before the first print but I can't get it to work in a way that as long as my

(n == sum) it prints Cycle of length 1: x x pairs

(n == res && sum < res) it prints Cycle of length 2: x y x pairs

(res <= MAXNUM) it prints Cycle of length c: x y z ... x (c amount of pairs including first x)

What do you guys think I should change?

Ok, this code should work if I understood well your requirement.

``````#include <stdio.h>
#include <stdlib.h>

int div_sum(int n)
{
long sum = 0;
int square_root = sqrt(n);

for (int i = 1; i <= square_root; i++)
{
if (n % i == 0)
{
sum += i;
if (i * i != n)
{
sum += n / i;
}
}
}
return sum - n;
}

int MAX_N = 10000000;
int MAX_CYCLES = 28;

int main()
{
int cycles;
for(int n = 2; n < MAX_N; n++){
int found = 0;
for(int c = 1; !found  && c <= MAX_CYCLES; c++){
cycles = c;
int aliquote = n;
while(cycles--) aliquote = div_sum(aliquote);

//it is a cycle of length c
cycles = c;
if(n == aliquote){
printf("Cycle of length %d: %d", c, n);
while(cycles--){
aliquote = div_sum(aliquote);
printf(" %d", aliquote);
}
printf("\n");
found = 1;
}
}
}
return 0;
}
``````
Source (Stackoverflow)